Remote Fourier ptychography at a distance of 3.2 km

Fourier ptychography (FP) enables synthetic-aperture resolution enhancement without direct phase measurement, but kilometer-scale implementation requires a stable experimental platform for controlled illumination, precise scanning, and consistent acquisition. Here, we report a facility-enabled demonstration of single-aperture scanning FP over a 3.2-km tunnel path. The tunnel-based testbed integrates high-power expanded laser illumination, large-aperture receiving optics, and a precision two-dimensional translation stage. Under weak-turbulence conditions, a 25 × 25 sub-aperture sequence was acquired, forming a 1560-mm synthetic aperture. The reconstruction image achieves a 3.6-fold improvement over the equivalent single-aperture image and a 2.5-fold enhancement beyond the diffraction limit.